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. 2010 Apr 22;21(1):103–114. doi: 10.1093/cercor/bhq063

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© The Authors 2010. Published by Oxford University Press.

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.5), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Figure 1. — Hierarchical organization of visual processing and models of stimulus type specificity. The left side of the figure illustrates the order of bottom-up processing of written words and pictures during our picture-naming task starting with visual input (bottom row) via posterior LvOT and anterior LvOT to speech output (top row), with many stages between anterior LvOT and speech output that are not considered here. In both the left and right side of the figure, posterior LvOT is illustrated below anterior LvOT and bottom-up processing is illustrated with upward arrows while top-down processing is illustrated with downward arrows. The upper right part of the figure shows our left occipito-temporal region of interest (in black), defined as activation for written words relative to fixation projected on a 3D brain. The rest of figure illustrates 5 different models of stimulus type specificity/nonspecificity in the LvOT cortex. The stimulus type specific models (A1 and A2) respond differently to words and pictures. The stimulus type nonspecific models (B1, B2, and B3) show common responses for words and pictures. Neuronal populations are circled separately for words (W) and pictures (P) when there is stimulus type specificity in the bottom-up processing stream. In contrast, neuronal populations for words and pictures are linked together (W and P) when bottom-up processing (from lower to higher) is not specific to stimulus type. Within stimulus type, connectivity between lower and higher levels is always assumed to be bidirectional (bottom up and top down). Top-down processing across stimulus type is indicated by dotted lines in the 3 models that are not specific to stimulus type (B1, B2, and B3). To summarize the distinction between the models: In A1, neuronal populations are specific to stimulus type at both levels of the hierarchy. In A2, neuronal populations are specific to stimulus type at the lower but not the higher level. In B1, B2, and B3, neuronal populations are not specific to stimulus type because of top-down processing across stimulus type. Nevertheless, there is stimulus type specificity in the bottom-up processing at both levels in (B1) and at the lower but not higher level in (B2).